The new hardware tessellation feature available on Direct3D 11 video cards has great potential, but using it effectively currently requires understanding higher-order surfaces as well as a myriad of performance implications. In addition to the Windows DirectX Graphics documentation, here are a number of resources for learning more about using Direct3D 11 Tessellation:

Gamefest 2008 - Direct3D 11 Tessellation
MS Downloads

Gamefest 2008 - Advanced Topics in GPU Tessellation (AMD/ATI)
MS Downloads

Gamefest 2008 - Water-Tight, Textured, Displaced Subdivision Surface Tessellation Using Direct3D 11 (NVIDIA)
MS Downloads

Game Developer Conference 2009 - Direct3D11 Tessellation Deep Dive
MS Downloads

Gamefest 2010 - Think DirectX 11 Tessellation! – What Are Your Options?
MS Downloads

The following samples:
DetailTessellation11, PNTriangles11, SimpleBezier11, and SubD11

NVIDIA and AMD also did a number of presentations at Game Developers Conference, including the following talks on Direct3D 11 Tessellation:

GDC 2010 - Enriching Details using Direct3D 11 Tesselation (NVIDIA)
NVIDIA Developer Website | AMD Developer Website

GDC 2010 - Tessellation Performance (AMD/NVIDIA)
NVIDIA Developer Website | AMD Developer Website

GDC 2010 - Direct3D 11 Tutorial: Tessellation (AMD) 
AMD Developer Website

GDC 2009 - D3D11 Tessellation (NVIDIA)
NVIDIA Developer Website | AMD Developer Website

GDC 2009 - Authoring for Real-Time Tessellation and Displacement Mapping (AMD)
AMD Developer Website

Related: Getting Started with Direct3D 11